In April at least 10 shopkeepers were conned into accepting forged £50 notes in Hull.

PC Martin Pepper, who led the fake currency probe, said: “When a counterfeit note reaches a bank it is taken out of circulation, leaving shopkeepers out of pocket.

“We are trying to educate as many companies and businesses as possible to prevent them being at a loss in the future.”

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Also in April, police in Hampshire found fake £50 notes had been used in shops and pubs.

Ex-credit fraudster Tony Sales, who now runs a fraud detection business in London, said: “Fake currency is big business for organised criminals and the counterfeit operations are becoming more sophisticated.”

In January, police in Naples seized five printing presses used to produce fake banknotes, plus unfinished fake €50 bills to the value of €50million.